# Post hoc, ergo propter hoc

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An example observed in the wild
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Post hoc, ergo propter hoc is a Latin phrase for "after this, therefore, because of this." The term refers to a logical fallacy that because two events occurred in succession, the former event caused the latter event.[1][2]

In addressing a post hoc, ergo propter hoc argument, it is important to recognise that correlation does not equal causation.

Magical thinking is a form of post hoc, ergo propter hoc fallacy, in which superstitions are formed based on seeing patterns in a series of coincidences. For example, "these are my lucky trousers. Sometimes good things happen to me when I wear them."

## Alternate names

• Assuming the cause
• Faulty Causal Assumption
• Post hoc

## Form of the argument

P1: X happened before Y.
P2: (unstated) Y was caused by something (that happened before Y).
C: Therefore, X caused Y.

### Other examples

Many superstitions use this. For instance, a black cat crosses my path on the way to school. I then fail a test that day. If I used this fallacy, I may conclude I failed because of the black cat, while ignoring other factors such as the amount of time I spent studying.

• The rooster crows before sunrise, therefore the crowing rooster causes the sun to rise.
• The drunk scientist conducts an experiment to see why he gets hangovers. He decides to keep a diary. Monday night, scotch and soda; Tuesday morning, hangover. Tuesday night, gin and soda; Wednesday morning, hangover. Wednesday night, vodka and soda; Thursday morning, hangover. Thursday night, rum and soda; Friday morning, hangover. On Friday night before going out for a drink, the drunk scientist has an epiphany. "Aha!" he says to himself, "I've got it! Soda causes hangovers!"
• A man takes a vaccine and dies weeks later. The cause is blamed on the vaccine, instead of pre-existing health conditions.[4]
• When compared on a graph, the number of deaths by falling and drowning in a swimming pool correlates with the number of movies that Nick Cage is in. This is completely coincidental… Unless it's not.[5]

## The obvious caveat

Note that this fallacy can be partly logically valid, in that "Every time I've seen an X, there was a Y nearby" is usually good cause for further investigation. For example, "Just about everybody I know who smokes Lucky Strike cigarettes gets lung cancer" was a valid place to start an investigation into what was later realized to be the smoking-cancer connection — although the causation was partly wrong: by no means was the connection confined to one brand.

Just keep in mind that the causation might be different than you might expect; for one obvious example, "fat people eat more diet food" does not mean "diet food causes fatness".[note 1] Our Correlation does not imply causation article has more on the various possible causality directions of a real correlation.